1. Field of the Invention
The present invention relates to data transmission in a Time Division Multiple Access (TDMA) system. More particularly, embodiments of the invention relate to methods for determining an inter-slot power level during data transmission in a TDMA system.
2. Related Technology
With advances in wireless communication technologies, various wireless communication standards with increasingly optimized data transfer rates have been developed. For example, the European Telecommunications Standards Institute (ETSI) has utilized a gaussian minimum shift keying (GMSK) scheme as a modulation scheme in Global System for Mobile Communication (GSM) systems. The ETSI has also utilized an 8-phase shift keying (8PSK) scheme as a modulation scheme in Enhanced Data rates for Global Evolution (EDGE) systems.
EDGE systems can be configured to transmit data modulated by multiple modulation schemes. For example, a first timeslot of data may be modulated using an “8PSK” modulation scheme and a second timeslot of data may be modulated using a “GMSK” modulation scheme. This example modulation scheme is known as an “8PSK+GMSK” dual modulation scheme. The period of time between the first and second timeslots in this example is known as an “inter-slot.” Typically the power level of the data transmission signal during an inter-slot in an EDGE system is determined using predetermined ramping values stored in memory.
This conventional approach of using predetermined ramping values in determining inter-slot power levels has at least three problems. First, the conventional use of predetermined ramping values in determining inter-slot power levels can cause power versus time (PVT) errors. Second, if a power level between timeslots is abruptly changed, a spurious signal can occur, resulting in increased data errors. Third, this conventional method may have a negative influence upon the switching characteristics between the first and second timeslots.
FIGS. 1 and 2 are waveform diagrams disclosing example cases in which data modulated by two different modulation schemes is transmitted. In FIG. 1, the data is transmitted by both modulation schemes at the same power level. In FIG. 2, the data is transmitted by each modulation scheme at a different power level. FIGS. 1 and 2 also disclose a PVT graph that represents data modulated by an 8PSK scheme that is transmitted to a first timeslot and data modulated by a GMSK scheme that is transmitted to a second timeslot.
As disclosed in FIG. 1, where the first timeslot power level is equal to the second timeslot power level, the inter-slot power level may be abruptly lowered during the inter-slot. The abrupt lowering of the power level during the inter-slot may result in a spurious signal. Furthermore, as disclosed in FIG. 2, where the first timeslot power level is significantly different from the second timeslot power level, an inter-slot power level may be abnormally determined due to the use of a predetermined ramping value in the determination of the inter-slot power level.
Hence, it would be desirable to provide the ability to determine an inter-slot power level dynamically using the actual power-levels of the surrounding timeslots in order to avoid spurious signals and abnormal inter-slot power level determinations.